In my first job on an electronics campus I suggested a day care centre to my HR manager because it was obvious 90% of the employees across all the factories were young females. Only about 1 in 50 engineers and technicians were female, but all the operators were (with their tiny little hands perfect for sewing gold thread) and all the HR staff (with their female capacity for faking empathy).
She ran with the idea and opened up a creche nearby and became a millionaire. My idea though, although I never earned a penny or even kudos from it.
Later, a half mile away, I came up with VoIP, and thought, "This will make for a fun office joke." Kind of scunnered when Skype sold to Microsoft for a billion.